[Null] has two contexts, one as a type and the other as a value (or more correctly, the unknown value).
All types in Lasso—string, array, map, etc.—can eventually trace down to a null ancestor. If a parent is not explicitly specified when a type is defined then the parent of the type is null.
[Null] itself represents a value that is unknown. [Null] is not zero, not an empty string, and is neither boolean True nor False. When a variable is defined without an initial value assigned to the variable, then the variable will have the default value of null.
Compare the local against [Null].
local(n) #n == null
Compare the type->parent method against 'null' (type->parent returns a string).
set->parent == 'null'
Please note that periodically LassoSoft will go through the notes and may incorporate information from them into the documentation. Any submission here gives LassoSoft a non-exclusive license and will be made available in various formats to the Lasso community.